Centrifugal compressor blading

ABSTRACT

A centrifugal compressor, which may otherwise be conventional, has the tip portion of the impeller blades made of a porous material to allow some of the air to flow from the forward face of the blade through the blades to the rear face to promote more uniform velocity at the impeller exit and thus reduce mixing losses and improve the slip factor of the compressor.

United States Patent 11 1 Bandukwalla 1 July 31, 1973 [54] CENTRIFUGALCOMPRESSOR BLADING 3,411,794 11/1968 Allen 416/95 X [75] Inventor:Phiroze Bandukwalla, lndianapolis, OR PATE TS 0R APPLICATIONS 112,26910/1964 Czechoslovakia 416/231 858,284 12 1952 G 416 185 [73] Assgnw g 92 860,898 12/1952 416/231 etmn 875,984 5/1953 Germany 416/231 22 Filed:Oct. 4 1971 1,046,247 12/1958 Gennany v 416/186 942,648 11/1963 GreatBritain 416/231 [21] Appl. No.: 186,302

' Primary Examiner-Everette A. Powell, Jr. 521 U.S. c1 416/183, 416/181,416/188, Ftzlamck 416/231 51 1111.01. Fold 5/04 [57] ABSTRACT [58] Fieldof Search ..4l6/l81183, A centrifugal compressor. which y Otherwise be185 1 13g 231 227 22 conventional, has the tip portion of the impellerblades made of a porous material to allow some of the air to 5 R f nCited flow from the forward face of the blade through the UNITED STATESPATENTS blades to the rear face to promote more uniform velocl 071 660 81913 B 4 ity at the impeller exit and thus reduce mixing losses l622930341927 ZEZE'Q 'Q' and improve the slip factor of the compressor.2,161,182 6/1939 Massey 416/231 UX 2 Claims, 4 Drawing FiguresCENTRIFUGAL COMPRESSOR BLADING The invention described and claimedherein was made in the course of work under a contract with theDepartment of Defense.

My invention relates to centrifugal compressors, and particularly to animprovement of the rotor blades of such compressors to improve flowconditions and therefore the efficiency and stability of operation ofsuch compressors.

Centrifugal compressors for air and other gases are very well known andwidely employed and have great advantages, particularly in lowerpressure ranges, because of the simplicity of their structure ascompared to axial-flow compressors.

Such a compressor is described in Atkinson U.S. Pat. No 2,819,012 forCentrifugal Compressor, Jan. 7, 1958. Air enters the compressor throughan annular entrance generally parallel to the axis of rotation and isaccelerated circumferentially of the rotor while moving radially outwardunder the influence of centrifugal force, the discharge of air from theimpeller being primarily tangential, with a substantial radial componentand ordinarily little axial component of velocity.

The high velocity discharge from the rotor or impeller is diffused instructure providing a diverging flow path and the dynamic head is thusin large measure converted to pressure head, so that the discharge is ata substantial rise in pressure above atmospheric or other inletpressure. Such compressors are found in gas turbine engines,turbochargers, air conditioning machines, and various otherenvironments.

Since the movement of the air is accomplished by the paddle-like actionof the face of a generally radial blade pushing the air generallytangentially, the flow in the space between adjacent blades in notuniform, the flow tending to concentrate on the forward or advancingface of the blade, where the air is at higher pressure and the velocityis greater than adjacent the rear or retreating blade face. Thus, withthe multibladed rotor, the discharge at any fixed point is to someextent pulsating, with greater radial velocity of discharge adjacent theforward face of each passing blade.

It has occurred to me that flow through the diffuser and, in general,the efficiency and resistance to surge of the compressor may be improvedby suitable expedients to smooth out the radial velocity of flow fromthe impeller without undue energy losses. This has led me to the conceptthat, by making the tip portion of the blades of a porous material sothat air may flow from the forward to the rear face of the blade throughpassages distributed over the area of the blade tip, the inequality offlow may be largely counteracted and the mixing losses in the space intowhich the air is discharged and the efficiency of the diffuser can besub stantially improved.

Having become aware of the existence of metallic materials having smallclosely distributed pores which have been developed for use astranspiration-cooled turbine blades, seals, and other hot parts ofturbine engines, I have concluded that a material of this generalcharacter will provide the requisite structural properties and thecontrollable porosity to implement my in vention.

Therefore, I propose to form the tips of centrifugal impeller blades oflaminated material having an array of fine closely distributed poresover the surface to provide for flow of air from the forward to the rearface of the blade for the reasons set out above.

I am aware of blowing slots in airfoils and of the slotted centrifugalrotor blades proposed by US. Pat. No. 2,819,838 of Warner, Jan. 14,l958.

The principal objects of my invention are to improve the performance andutility of centrifugal compressors, to provide smoother flow in thedischarge from a centrifugal compressor rotor, and to provide animpeller structure with porous blade tips which is readily fabricatedand which will withstand the forces encountered in operation.

The manner in which these and other objects of my invention areaccomplished and the nature of the invention will be apparent to thoseskilled in the art from the succeeding detailed description of preferredembodiments of the invention and the accompanying drawings thereof.

FIG. 1 is a partial sectional view of a centrifugal compressor, takenprincipally on a plane containing the axis of rotation.

FIG. 2 is a greatly enlarged view of a portion of FIG. 1.

FIG. 3 is a view similar to FIG. 2 of a modified structure.

FIG. 4 is a partial sectional view taken on the plane indicated by thefirst line 44 in FIG. 2.

Referring first to FIG. 1, the centrifugal compressor, illustrated moreor less schematically, comprises a housing 2 having a front wall'3 and arear wall 4. A rotor or impeller 6 disposed between the walls issuitably fixed to a shaft 7. The shaft is rotatably supported in abushing 8 mounted in a bearing support 10 suitably supported from thefront wall and in a bushing 11 mounted in the rear wall 4. The frontwall 3 and bearing support 10 define an annular air entrance or eye 12.The front and rear walls define between them a diffuser or diffusingspace 14, which may have any suitable configuration, only the inner partof which is illustrated.

The rotor 6 comprises a hub or disk 15 fixed on shaft 7. The hub definesthe inner and rear boundary of the gas flow path through the compressorrotor. The front wall 3 defines the outer and forward boundary of thisflow path.

The air is moved by a ring of generally radially extending blades 16,the initial portions of which, as shown in the lower portion of FIG. 1,are curved forwardly to act as the inducer portion of the impeller andthe rear or radially outer portions of which lie approximately orexactly in surfaces parallel to the axis of the shaft 7. The bladesterminate at a tip 18 which may be at the same radius as the peripheryof the disk 15.

The structure so far described is known, and may be the same as thatdescribed at greater length in the aforementioned Atkinson patent.

My invention is embodied in the portion of each blade adjacent the tip18, which we may call the tip portion 19, and which may preferablyinvolve approximately the outermost 10 percent of the radius of theimpeller. Referring to FIGS. 2 and 4 for details of structure, FIG. 4illustrates a blade having a slightly forward leaning tip, but the tipmay be strictly radial or backward leaning so far as the presentinvention is concerned. However, I beleive it to be more beneficial witha forward-raked blade.

The tip portion 19 of the blade is a laminated porous body comprisingthree sheets; a from sheet 20, a middie sheet 22, and a rear sheet 23.All of these sheets bear a two-dimensional array of closely spacedperforations 24 with the perforations in each registering with those inadjacent sheets so that numerous small pores are provided through thetip portion. One such pore is indicated by the arrow 26 in FIG. 4. Itwill be understood that the structure is greatly enlarged for clarity ofdelineation in FIGS. 2 and 4. The sheets 20, 22, and 23 may be of theorder of 0.010 inch thick and the perforations of about the samediameter. The several sheets may be brazed, diffusion bonded, orotherwise fixed together into a unitary structure. The perforations maybe made in any suitable manner, including photoetching or whatevertechnique is suitable to the materials involved. Preferably, theperforations are aligned somewhat out of register so that the trend ofthe pores 26 is radially outwardly from the forward to the rear face ofthe tip portion so that the air flowing through these pores from thehigh pressure face of the blade to the lower pressure face has aradially outward component of How Because of the substantial centrifugalforce, a positive attachment of the tip portion to the body of the blade16 is required. One mode of retention which is favorably regarded isshown in FIGS. 2 and 4. In this case, the middle sheet 22 has an innerborder at 27 radially outward of the inner borders of the other sheets.Holes 28 are etched, punched, or otherwise provided in the two outersheets. The impeller is bicast to the tip portion so that the metal ofthe impeller blade 16 extends into the gap between the front and rearsheets and forms bosses 30 extending into theholes 28 locking the tipportion onto the body of the blade.

HO. 3 illustrates a modified structure in which a tip portion 32 hasdovetail slots 34 cut in the radially inner margin of the front and rearsheets, these dovetail slots being filled with dovetails 3S integralwith the blade 16 when the impeller is cast.

Obviously, other modes of retention may be employed suited to theparticular installation. For example, with rotor structures of somematerials, the tip may be spot-welded to the rotor or a pinnedconnection may be used.

FIG. 2 illustrates another feature of structure which may be employed.In this case, a slot 36 is provided between the disk and the tip portion19 which also provides for flow of air from the leading to the trailingface of the blade. This slot in the example discussed might beapproximately 0.010 inch in width. The provision of a slot at thejunction of the blade tip and disk is, however, the subject matter of mypatent application Ser. No. 186,303 filed Oct. 4, l97l.

It may be noted that it is preferred to have the porosity of the tipportion increased towards the tip, either by having larger pores towardthe tip or by closer spacing of the pores.

in the operation of the compressor, the air under higher pressure at theforward face of the blade is forced by the pressure differential acrossthe blade through the blades so that some of this air emerges at thetrailing face of the blade and adds to the flow at this point. Byreducing flow at the forward face and increasing flow at the rearwardface, the disparity between radial flow rates across the gap betweenadjacent blades is very substantially reduced and flow patterns areimproved.

The detailed description of preferred embodiments of the invention forthe purpose of explaining the principles thereof is not to be consideredas limiting or restricting the invention, since many modifications maybe made by the exercise of skill in the art.

I claim:

1. A centrifugal compressor rotor mounted for rotation about an axis andincluding fluid-impelling blades adapted to impel fluid flowing radiallyoutward from the axis circumferentially with respect to the axis, theblades extending generally parallel to the axis and generally radiallyfrom the axis and terminating in blade tips generally parallel to theaxis at the extremity of the blades remote from the axis, the portion ofeach blade adjacent the tip being a laminated structure of plural layersof sheet metal having an array of numerous distributed pores extendingthrough the structure from the forward face to the rearward face toallow diffusion of air through the blade tip in response to the pressuredifferential across the blade, the pores being defined by communicatingperforations in the layers, and the per forations being so overlappedthat each pore extends radially outwardly from the forward to therearward face.

2. A centrifugal compressor rotor mounted for rotation about an axis andincluding fluid-impelling blades adapted to impel fluid flowing radiallyoutward from the axis circumferentially with respect to the axis, theblades extending generally parallel to the axis and generally radiallyfrom the axis and terminating in blade tips generally parallel to theaxis at the extremity of the blades remote from the axis, the portion ofeach blade adjacent the tip being a laminated structure of plural layersof sheet metal having an array of numerous distributed pores extendingthrough the structure from the forward face to the rearward face toallow diffusion of air through the blade tip in response to the pressuredifferential across the blade, the pores being defined by communicatingperforations in the layers, and the porosity of the tip portionincreasing in the direction toward the blade tip.

i t i t

1. A centrifugal compressor rotor mounted for rotation about an axis andincluding fluid-impelling blades adapted to impel fluid flowing radiallyoutward from the axis circumferentially with respect to the axis, theblades extending generally parallel to the axis and generally radiallyfrom the axis and terminating in blade tips generally parallel to theaxis at the extremity of the blades remote from the axis, the portion ofeach blade adjacent the tip being a laminated structure of plural layersof sheet metal having an array of numerous distributed pores extendingthrough the structure from the forward face to the rearward face toallow diffusion of air through the blade tip in response to the pressuredifferential across the blade, the pores being defined by communicatingperforations in the layers, and the perforations being so overlappedthat each pore extends radially outwardly from the forward to therearward face.
 2. A centrifugal compressor rotor mounted for rotationabout an axis and including fluid-impelling blades adapted to impelfluid flowing radially outward from the axis circumferentially withrespect to the axis, the blades extending generally parallel to the axisand generally radially from the axis and terminating in blade tipsgenerally parallel to the axis at the extremity of the blades remotefrom the axis, the portion of each blade adjacent the tip being alaminated structure of plural layers of sheet metal having an array ofnumerous distributed pores extending through the structure from theforward face to the rearward face to allow diffusion of air through theblade tip in response to the pressure differential across the blade, thepores being defined by communicating perforations in the layers, and theporosity of the tip portion increasing in the direction toward the bladetip.